This invention relates to carburetors and, more specifically, to a carburetor improvement by which the mechanism controlling opening of the carburetor choke valve is made tamper resistant.
An important area in controlling automobile engine exhaust emissions is calibrating various components of a carburetor installed on the engine so in their normal course of operation the air-fuel ratio of the mixture produced by the carburetor and supplied the engine is maintained within certain specified limits. In this regard, control of a carburetor's choke valve opening is especially important because of the high level of emissions which are produced during engine starting and warm up.
Choke valve operation on a carburetor involves two stages. The first stage occurs when the engine is started and the choke valve is pulled from its closed or substantially closed position to a first open position. The second stage involves the gradual movement of the choke valve from its first open to its fully open position as the engine warms up. Conventionally, the mechanism employed during the second stage involves a thermostatic coil acting on a lever which, in turn, controls rotation of a shaft on which the choke valve is mounted. On some carburetors, this lever does not act directly on the choke shaft, but rather is connected, via a rod or link, to a second lever which is attached to the choke shaft. During qualification of a carburetor of this type, a gage is used to set the lever and the rod or link is bent to adjust the position of the lever relative to the coil. When the proper relationship is established, the controlled opening of the choke valve is such as to produce an air-fuel mixture which is not excessively rich so engine emissions remain within specified tolerances.
A disadvantage of the above-described procedure is that the rod or link remains accessible after the carburetor is installed on an engine. Thus, someone can bend the rod or link so as to change the adjustment of the lever with the result that during choke valve opening an excessively rich air-fuel mixture is produced which, in turn, causes excessive engine emissions.